Organic coating composition



United States Patent C ORGANIC COATING COMPOSITION Thomas L. Canuifr andAlfred E, Balocca, Wheaton, Ill., assignors to American Can Company, NewYork, N.Y., a corporation of New Jersey No Drawing. Application May 28,1953 Serial No. 358,170

6 Claims. (Cl. 99-181) The present invention relates to a novel,economical and effective coating composition. More particularly thepresent invention pertains to a modified styrene-diolefin copolymercoating composition for sheet metal, and especially containersfabricated from ferrous metal sheets.

The use of organic coatings on sheet metal as a protection therefor isold and well known. However due to the unique problems in canmanufacture, relatively few of theknown coating compositions areapplicable to can making. The maximum thickness of the coating on metalcans is but a fraction of the usual thickness of the coatings on othermetal surfaces. This extremely thin coating must be hard so as to resistmarring during abuse in fabrication and handling of the cans; it must beflexible in order to form a continuous adherent film over can parts thathave been fabricated by drawing or bending; and. it must besubstantially impervious to chemical attack. In relation to the lastrequirement, such a variety of products are packed in cans eachpresenting its own corrosive problem. Heretofore there has been nosingle organic coating composition that is effective against thedifferent types of chemical attack. Therefore it is necessary "todevelop and use a different coating to resist each particular type ofcorrosion. Obviously such an operation is costly and troublesome.

During recent years this situation has been aggravated by the tremendousincrease in the use of organic coatings over tin coatings. Previouslymost, if not all metal containers were made from sheet steel having aprotective coating of tin on its surfaces. This involved atremendous'consumption of tin in view of the fact that billions of metalcontainers are manufactured each year. Due tothe growing scarcity oftin, aconstant effort has been made by the container manufacturingindustry to develop substitute coating compositions and methods by whichto conserve tin or obviate its use entirely. In relation to protectivecoatings for steel plate, one method Q ti c nse t on has b e t duce rasc ly the weight of tin deposited on sheet steel and provide supplementalprotection by the use of organic coatings thereover, Another method hasbeen to eliminate entirely the use of tin coating and obtain corrosionprotection solely by the use of organic coatings.

We have discovered that by modifying a particular styrene-diolefincopolymer with a. small amount of an acidic phosphorus compound andthereafter applying this novel composition to the surface of a ferrousmetal plate and treating the coated plate we produce a thin, hard,adherent, flexible film thereon which protects the metal substrate fromatmospheric and other chemical corrosion.

Therefore an object of this invention is to provide a substantiallyuniversal organic coating for metal containers.

Another object of this invention is to provide a sub stantiallyuniversal organic coating for metal containers that is equivalent inquality and protective value to tin coated containers and which is morereadily available and less costly than tin.

, Another object of this invention is to provide a substantiallyuniversal organic coating for ferrous metal containers and many otherferrous products that is more coonomical and in many respects superiorto organic coatings presently in use.

, A further object'of this invention is to provide a substantiallyuniversal, tough and flexible organic coating for all types offabricated sheet metal products which in the course of manufacture haveto undergo considerable bending and shaping operations.

The particular copolymer useful in the present invention is a syntheticdrying oil. In its preparation, to parts by weight of butadiene and 25to 15 parts of styrene, preferably 80 parts of the former with 20 partsof the latter are copolymerized in the presence of metallic sodium and areaction diluent at a temperature below the melting point of thecatalyst. Temperatures from 25 C. to C. are operable with temperaturesbetween 40 C. and 80 C. particularly preferred. The quantity of catalystis about 0.5 to 5 parts and preferably from 1 to 3 parts of finelydivided sodium per parts of monomer.

While styrene yields the best product, it is possible in some instancesto substitute for all or part of the styrene its paraor metaloweralkylated homologues, e.g. para-methyl styrene, meta-methyl styrene,dimethyl styrene, and the corresponding ethyl-substituted homologues.Alpha-substituted styrenes are useless and inoperative because of theirpoisoning effect on the polymerization reaction.

As with styrene, butadiene produces the best results. However, here alsoin some instances the butadiene may be replaced in whole or in part byisoprene, 2,3-dimethyl butadiene-1,3-piperylene, or Z-rnethylpentadiene-l,3.

The diluent used in the reaction is important. Inert diluents having aboiling range between 20 C. and 200 C. may be used with aliphatichydrocarbons being preferred, e.g. solvent naphtha, mineral spirits suchas Varsol (boiling range about C. to 200 C.), Solvesso (boiling rangeabout 95 to 200 C.). Aromatic solvents such as benzene, toluene andXylene may also be used but are not as desirable as the aliphaticsolvents due to their toxicity. These hydrocarbon diluents are used inamounts ranging from 100 to 500, preferably 200 to 300 parts per 100,parts of monomers. An improvement in the polymerization rate andproduction of a colorless copolymer can be obtained by using with theaforementioned hydrocarbon diluent, a substantial amount of a C to Caliphatic ether, a nonaromatic cyclic ether or a polyether other thanthose having an -OC0- grouping. Particularly effective among these isdioxane-L4. Other examples of ethers producing favorable results are thediethyl ether of ethylene glycol, diethyl ether of dietbylene glycol anddiethyl ether. Still other ethers useful to a lesser extent are diethylacetal, vinyl isobutyi ether, dihydropyrane, and isopropyl ether. Ingeneral the ethers tried and found to beprcferred are cyclic diethers of4 to 8 carbon atoms wherein the two oxygen atoms ar separated by atleast two carbon atoms, and also saturated aliphatic ethers having theformula C H O(C H O),,C H wherein n is an integer from 0 to 2 inclusive.The ether co-diluent is used in amounts ranging from about 10 to 45, andpreferably from 25 to 35 parts per 100 parts of monomers. For easyrecovery from the reaction mass, the ether should have a boiling pointat least 10 C. below the lower limit of the hydrocarbon diluent boilingrange.

As a catalyst promoter, especially when using a coarser catalystdispersion, it is advantageous to use about l%, ,to 50% by weight ofcatalyst, of a C to C aliphatic alco,-. hol, preferably a secondary ortertiary aliphatic alcohol. Weight percents of 10% to 20% of thecatalyst, or about 0.1 to 1 Weight percent based on the monomers ispreferred. Examples of such alcohols are isopropanol, secbutanol ortert-hutanol or in some instances n-propanol or n-pentanol.

In the preferred method of carrying out the reaction, an autoclaveequipped with a mechanical agitator is used. The autoclave is chargedwith the butadiene feed in a portion of the diluent and with the sodiumcatalyst. It is desirable to operate with a catalyst particle size ofabout 1 to 100 microns, preferably about to 50 microns. The catalyst isusually fed to the reaction as a slurry of metal particles dispersed in2 to 200 parts of a hydrocarbon diluent. This feed is then brought up toreaction temperature thereby initiating the polymerization of thebutadiene. The styrene in the remainder of the liquid diluents is thenfed into the autoclave. The lapse of time between the butadiene feed andstyrene feed is usually from 10 to 60 minutes. The copolymerizationreaction time varies with the reaction temperature and catalyst particlesize, i.e. about 40 hours at 50 C. with a coarse catalyst to aboutminutes at 95 C. with a catalyst particle size of less than 100 microns.At the end of the reaction, the catalyst is destroyed by treating thereaction mass with a slight excess of an acid such as glacial aceticacid. The mass is then neutralized as with ammonia and the neutralizedproduct is filtered. The filtered mass is subjected to distillation toconcentrate the product to a solution of 50% to 70% non-volatile matterin hydrocarbon solvent.

The resulting produce is a clear, colorless to light yellow compositionhaving a viscosity of about 0.5 to poises preferably 1 to 10 poises at50% non-volatile con-- tent. The Staudinger molecular weight of thenon-volatile content or polymeric product falls between 1500 and 5000,preferably about 1800.

The addition of from 0.01% to 2.5%, preferably from 0.05 to 0.50% ofunsaturated anhydride, such as maleic, chloromaleic, or citraconicanhydride to the copolymer improves its properties as a vehicle forpigments. This anhydride may be added to the reaction mass during theformation of the copolymer or may be blended with the finished copolymerin a suitable well-known manner.

The above described copolymers are more fully described in copending US.patent application Serial No. 102,703, filed July 1, 1949, now Patent2,652,342, and application Serial No. 176,771, filed July 29, 1950, nowPatent 2,762,851.

The above described copolymer, while showing promise as an organiccoating for metal containers is deficient in that regard in manyimportant factors, e.g. blistering. discoloration, adhesion andespecially flexibility. This last deficiency results in the corrosion ofcontainer parts fabricated from plate having the unmodified copolymer asa coating thereon due to fracture of the coating at points where thesubstrate metal was subjected to stress or bending. We have discoveredthe surprising and unexpected fact that the addition of a small amountof an acidic phosphorus compound to the copolymer alleviates thesedeficiencies yielding a composition having in all respects exceptionalproperties as a metal container coat-- ing. It is believed that thisremarkable improvement is due to the acidic phosphorus compoundinhibiting oxidative polymerization of the cross-linking type during thecuring of the film thereby yielding a less brittle, more adherent andmore fiexible film. However, since these theoretical considerations formno part of the present invention, we do not Wish to be bound thereby.

The term acidic phosphorus compound used herein designates phosphorusacids, phosphorus acid derivatives having at least one replaceableacidic hydrogen atom and mixtures thereof. Included in the phosphorusacids are ortho-, meta-, hypo-, and pyrophosphoric acid, phosphosphorousacids, polyphosphoric acid and any phosphorus compound that will yield aPhosphoric acid in aqueous solution, e.g. hydrates of orthophosphoricacid,

anhydrous phosphoric acid, phosphorus pentoxide, phosphoric oxide,phosphoric anhydride, P 0 and P 0 Of the phosphorus acid derivatives weinclude: inorganic salts of phosphorus acid such as zinc acid phosphateand ammonium acid phosphate; organic esters of phosphorus acids such asalkyl phosphates, e.g. n-amyl phosphate and dibutyl phosphate; andorganic salts of phosphorus acids such as amine phosphates, e.g. mono-(dibutylamine) pyrophosphate, dianiline phosphate and dibenzylaminephosphate. Of the acidic phosphorus compounds disclosed, theunsubstituted phosphorus acids are preferred.

In accordance with the invention the acidic phosphorus compound isdissolved in a suitable solvent. An amount of this solution is slowlyadded to an already prepared solution of the copolymer so that theresulting product contains a major portion of copolymer and a minorportion of acidic phosphorus compound. Based upon the weight ofcopolymer in the composition, between 0.1% and 10% of acidic phosphoruscompound and preferably between 0.50% and 4.0% is incorporated in thecomposition. These limits are critical since an amount of acidicphosphorus compound less than the minimum limit fails to give thedesired result and an amount thereof greater than the upper limitinhibits curing of the film to an excessive degree causing it to be softand tacky. If the acidic phosphorus compound solution is insoluble inthe copolymer solution, the addition must be accompanied by vigorousagitation of the mass so that the former is uniformly dispersedthroughout the latter yielding a homogeneous product. However, withcertain acidic phosphorus compounds, e.g. some organic phosphates, asolvent compatible with the resin solution can be used so that a clearsolution of acidic phosphorus compound solution in copolymer solutioncan be obtained. With other acidic phosphorus compounds, it may beadvantageous to add them as a solid or in the form of a thick slurry.This may be accomplished by milling the acidic phosphorus compound intothe copolymer. The time of mixing or temperature of the ingredients isnot critical varying over a wide range. The only limitation as to timeof mixing is that sufficient time be allowed to insure uniform andintimate contact of the ingredients. In general 5 to 15 minutes shouldbe suflicient. As to temperature, it is necessary only that thesolutions be liquid, i.e. above their freezing points.

Solvents such as water, lower aliphatic alcohols, normally liquidketones and combinations thereof can be used as solvents for the acidicphosphorus compound. As a solvent for the copolymer, the hydrocarbondiluents described hereinbefore are satisfactory. In the acidicphosphorus compound modification of the copolymer the selection of aproper solvent is not critical depending merely upon the degree ofsolubilities of the respective ingredients therein.

In the coating operation, the metal sheet may be either spray, dip orrolled coated. The procedure generally used in metal containermanufacture is the roller coating of flat, metal sheets as by anapparatus similar to that disclosed in United States Patent 1,848,856issued to C. Wagner et al. on March 8, 1932. The resin coating is thencured at an elevated temperature usually by means of a device similar tothat shown and described in United States Patent 1,293,261, issued to C.Wagner et al. on February 4, 1919.

In applying the coating composition of the present invention by theroller coating process, the liquid coating composition should have aviscosity of between and 315 centistokes and preferably between and 250centistokes and a solids content of not less than 20 percent by weightof the total, liquid composition. In actual operation the solids contentis in the range of 40 percent to 60 percent by weight of the total. Toeffect a cure, the resin coating is baked at a temperature of from 375'F. to 420 F. for 10 to 15 minutes. The cured film approximately from2.5X- to 8.5)(10' cm. thick ranging upward therefrom t5 unsatisfactory.rating Over the t sub ra a d has w sh approximately at abo t e n tt l aac y- Table l v ilumpk .0m

Coating Metal Substrate f v Process Flexib. Process Flexib.

Resist. Resist.

unmodified copolymer CMQ 12. 3 23. 4 7. 3 15. 0 Do low weight tin plate4. 1 5. 6 6. 3 6. 4 comm'l corn can matin CM D low eight tin plate 5.36. 0 6. 3 5. 6 high weight tin plate- 8.3 6. 3 7. 3 6. 4 CMQ low weighttin plate.- 5. 0 6. 9 comml pumpkin. high weight tin plate. 3.0 6.0modified copolyme CMQ 3. 0 5. 6 0. 3 6.3 Do low weight tin plate 3. 75.6 3. 9 6. 3

1 Unsatisfactory.

of from 2 mg. per square inch to 5 mg. per square inch respectively ofmetal plate surface.

The following tabulation will serve to illustrate specific While thenovel composition of the present invention has been describedspecifically as a metal can coating, it has utility of much greaterscope. This copolymer forms embodiments of the present invention but arein no way an excellent protective coating on all metal substrates,

intended as limitations thereon. In each of the following examples, themajor constituent of the composition is a styrene-butadiene copolymer asdescribed hereinbefore:

particularly ferrous metal substrates, where a tough, flexible,adherent, corrosion resistant, continuous film is desired.

Examples Percent Percent Viscosity No. Modifier Modifer Solvent Solid ofin Centiadded 1 Compostokes sition 1 o-phosphoric acid 1, 2, 4 ButanolToluene. 235 phosphorous acid 1, 2, 4, 6, 8, 10 d0 40 235 polyphosphoiicold. 1, 2. 4 40 235 dibutylphosphate 1, 2, 4 235mono-(dibutylaminel-pyrophos 1ate 1, 2, 4 .do 40 235 zinc dlhydrogenphosphate Zn( 1104); l, 2, 4 Mineral-Spirits.-- 40 235 dianilinephosphate 1, 2, 4 Buttimlol mineral- 40 235 51) r t5. mono-dihenzylaminephosphate 1, 2, 4 do 40 235 diammonium hydrogen phosphate 1, 2, 4, 6, 8,10 isopropanol tolu- 40 235 4):HPO4. ene wetting agent water.

Each num her represents a different composition having that percent byweight of copolymer of the particular acidic phosphorus compounddesignated.

8 This represents percent by weight of total composition.

Small amounts of other substances may be incorporated into the novelcomposition of the present invention depending upon the result desired.Included in these are It is thought that the invention and many of itsattendant advantages will be understood from the foregoing description,and it will be apparent that various changes pigments such as aluminumoxide and titanium oxide; 55 may be made in the matter of theingredients, their idenwaxes as internal lubricants; inhibitors; anddrying oils.

The data tabulated below shows the superiority of the coating of thepresent invention over all the other coatings rated on the productsshown thereby illustrating its value as a single replacement for thedifferent coatings tity and their proportions without departing from thespirit and scope of the invention or sacrificing all of its materialadvantages, the form hereinbefore described being merely a preferredembodiment thereof.

We claim:

1. A package comprising a comestible enclosed within a container, saidcontainer having a tubular metal body coated on its inside surface witha solid protective film comprising a substantially colorless sodiumcatalyzed copolymer consisting essentially of from 15 to 25 parts byweight of a monoaryl vinyl hydrocarbon and from 85 to 75 parts by weightof an aliphatic diolefin having 4 to 6 carbon atoms, and from 0.1 to 10%by weight based on said copolymer of an acidic phosphorus compound, saidcopolymer having a molecular weight of tainer parts and contacted withthe products designated from 1500 to 5000.

below, each coating receiving identical treatment in its contact withthe respective products. The coated metal can part was then removed fromthe product and evaluated, the results of which are shown in Table Ibelow.

2. The package set forth in claim 1 wherein said monoaryl vinylhydrocarbon is styrene and said aliphatic diolefin is butadiene.

3. The package set forth in claim 1 wherein said In the numericalratings given in Table 1, zero is perfect monoaryl vinyl hydrocarbon isstyrene, said aliphatic diolefin is butadiene and said acidic phosphoruscompound is selected from the group consisting of an unsubstituted acidof phosphorus, a phosphorus acid salthaving at least one replaceableacidic hydrogen atom, and mixtures thereof.

4. The package set forth in claim 3 wherein the unsubstituted acid ofphosphorus is ortho phosphoric acid.

5. The package set forth in claim 3 wherein the unsubstituted acid ofphosphorus is phosphorus acid.

References Cited in the file of this patent 6. The package set forth inclaim 3 wherein the unsub- 10 2,741,397

stituted acid of phosphorus is polyphosphoric acid.

V -UNITED STATES PATENTS Rothrock Aug. 12, 1941 Frolich et a1 Mar. 21,1950 Hunter Feb. 26, 1952 Kalafus Nov. 25, 1952 Crouch Mar. 10, 1953Gleason July 6, 1954 Shotton Apr. 10, 1956

1. A PACKAGE COMPRISING A COMESTIBLE ENCLOSED WITHIN A CONTAINER, SAID CONTAINER HAVING A TUBULAR METAL BODY COATED ON ITS INSIDE SURFACE WITH A SOLID PROTECTIVE FILM COMPRISING A SUBSTANTIALLY COLORLESS SODIUM CATALYZED COPOLYMER CONSISTING ESSENTIALLY OF FROM 15 TO 25 PARTS BY WEIGHT OF A MONOARYL VINYL HYDROCARBON AND FROM 85 TO 75 PARTS BY WEIGHT OF AN ALIPHATIC DIOLEFIN HAVING 4 TO 6 CARBON ATOMS, AND FROM 0.1 TO 10% BY WEIGHT BASED ON SAID COPOLYMER OF AN ACIDIC PHOSPHORUS COMPOUND, SAID COPOLYMER HAVING A MOLECULAR WEIGHT OF FROM 1500 TO
 5000. 